Search

Temporal solitons can arise in spectrally confined cavities with no chromatic dispersion. When the filter order tends to infinity, the soliton tends to a Nyquist pulse with a fully confined ultra-flat spectrum and a transform-limited waveform.

We propose an ultra-wideband photonic compressive receiver based on random codes shifting with image-frequency distinction. By shifting the center frequencies of two random codes in large frequency range, the receiving bandwidth is flexibly expanded. Simultaneously, the center frequencies of two random codes are slightly different. This difference is used to distinguish the “fixed” true RF signal from the differently located image-frequency signal. Based on this idea, our system solves the problem of limited receiving bandwidth of existing photonic compressive receivers. In the experiments, with two channels of only 780-MHz outputs, the sensing capability in the range of 11–41 GHz has been demonstrated. A multi-tone spectrum and a sparse radar-communication spectrum, composed of a linear frequency modulated (LFM) signal, a quadrature phase-shift keying (QPSK) signal and a single-tone signal, are both recovered.

In this paper, we proposed a tunable K/W-band OFDM integrated radar and communication system based on Optoelectronic Oscillator (OEO) for intelligent transportation. All-optical signal processing including amplitude asymmetric filtering and quadratic phase manipulating is applied in OEO to achieve a high-frequency and tunable self-excited oscillation, which supports the K/W-band OFDM signal generation. Its product of maximum detection range and communication capacity is cB/4Δf (m·Gbaud), where c is light speed and Δf is subcarrier spacing of OFDM. A proof-of-concept experiment is carried out in K-band with bandwidth B = 2 GHz and W-band with bandwidth B = 10 GHz. The range resolution ΔR, detection range Rmax and communication capacity C of 0.075 m, 75 m, 12.8 Gbps, and 0.015 m, 300 m, 32 Gbps are experimentally demonstrated in K/W-band respectively.

Existing photonic compressive receivers have the problem of resolution deterioration when applied in wide-range radar detection. In this study, we propose a photonic-assisted space-frequency two-dimensional (2D) compressive radar receiver capable of achieving high-resolution detection in wide-range scenarios. For the space dimension, the compression process is realized by employing a spatially adaptive photonic projection basis, which guarantees complete mapping of arbitrarily delayed echoes—the key to high-resolution wide-range detection. For the frequency dimension, photonic compressive sensing is employed to further compress the bandwidth of the projected sparse signal. Therefore, the proposed system can achieve wide-range radar detection without resolution deterioration with compressed output. Herein, with two channels of 630 MHz outputs, high-resolution distance detection within a range of 21 km with a resolution of up to 2.3 cm is achieved. Moreover, inverse synthetic aperture radar (ISAR) imaging of two sets of four-point turntables distributed within the range of 21 km with a resolution of 2.3 cm × 5.7 cm is realized. The proposed photonic-assisted 2D compressive radar receiver is a viable solution to overcome the tradeoff between detection resolution and range of existing photonic compressive receivers, which indicates a path for the further development of high-resolution wide-range radar detection.

In this paper, a broadband photonic beam processor is presented for the all-optical multifunction integrated receiver. By implementing echo signals with optical beam multi-domain processing based on space-to-time mapping and time-to-frequency mapping, the non-mechanical control of expected beam pointing is enabled while the target within the beam can be imaged simultaneously. A proof-of-concept experiment with a 4-element phased array is performed in Ka band. The beam pointing is set to be 0° and 12.5°, where two-dimensional images of moving targets inside the beam region are obtained, respectively. The suppression ratio to the beam region outside is measured to be 26.8 dB. And the range and cross-range imaging resolution is 0.042 m × 0.051 m. A comparison with a cascade mode of single-function microwave photonic modules shows that the multifunction integrated photonic beam processor has reduced the system loss by 32.4 dB. The proposed beam processor enables multi-element broadband phased arrays with less complexity and power consumption.

We propose a microwave photonic 2D time-frequency filter based on a photonic time-frequency prism. A time-varying frequency response is realized by deviating the passband of a 1D ordinary frequency filter in the 2D time-frequency plane. The proposed time-frequency filter features highly reconfigurable frequency-sweeping speed and bandwidth, thanks to the software-defined photonic time-frequency prism. With the proposed technique, separation of multiple linear and nonlinear chirp signals with overlapped spectra is experimentally demonstrated.

Three-dimensional (3D) imaging radar is an advanced sensor applied in space surveillance and target recognition for supplying 3D geometric features and supporting visualization. However, high 3D resolution requires both broadband operation and a large 2D aperture, which are difficult and complex for conventional radars. This paper presents a photonics-enabled distributed multiple-input and multiple-output (MIMO) radar with a centralized architecture. By use of photonic multi-dimensional multiplexing, multi-channel signal generation and reception are implemented on a shared reference signal in a central office, enabling a highly coherent network with a simple structure. Additionally, a sparse array and a synthetic aperture are combined to efficiently reduce the required transceivers, further weakening the dilemma between system complexity and angular resolution. A 4 × 4 MIMO radar is established and evaluated in field tests. A high-resolution 3D image of a non-cooperative aircraft is obtained, in which rich details are displayed. From a comparison with electronics-based radar, significant resolution improvement is observed. The results verify the superior imaging capability and practicability of the proposed radar and its great potential to outperform conventional technologies in target classification and recognition applications.

In this paper, we propose and demonstrate a novel spectrum stitching method for broadband linear frequency-modulated waveform (LFMW) generation. An optical frequency comb (OFC) is modulated by a narrowband LFMW whose bandwidth matches the free spectral range of the OFC. Optical injection locking is employed in extracting one broadband frequency sweeping component from the modulated OFC. In this way, seamless spectrum stitching is realized and a broadband LFMW with a multi-fold time-bandwidth product (TBWP) is obtained. Our scheme has a simple structure, which requires only a single OFC, a modulation module and a baseband waveform generator. An LFMW as broad as 20 GHz is generated from a baseband LFMW with 2GHz bandwidth experimentally. The TBWP is 100 times as large as that of the baseband LFMW. Moreover, the power fluctuation and the phase jumps are both eliminated, ensuring an excellent pulse compression performance. Benefiting from the injection locking technique, the linearity reaches 2.0 × 10−6. The central frequency tuning ability of our scheme is also demonstrated.

A novel, to the best of our knowledge, scheme for reconfigurable radar signal generation is proposed based on the principle of photonic phase-quantized digital-to-analog conversion. Multi-level digital phase modulation with different modulation depths is combined to convert multi-channel digital data to the phase of an optical carrier. Frequency-modulated or phase-modulated radar signals are generated by beating the phase-synthesized optical carrier with a coherent reference light. The proposed radar signal generator features a simple structure, highly reconfigurable modulation format, and flexibly tunable frequency. A 3-bit photonic phase-quantized digital-to-analog converter with a 10-GSa/s sampling rate is constructed experimentally. The generation of linear frequency-modulated, nonlinear frequency-modulated, frequency-stepped, frequency-hopping, binary phase-coded, and polyphase-coded waveforms is demonstrated.

In this paper, we propose and demonstrate a novel photonics-enabled frequency multiplication system with an ultrahigh multiplication factor (MF) for broadband linear frequency modulated (LFM) microwave generation. A pair of distributed feedback (DFB) lasers are injection-locked to two optical sidebands with different orders, which are excited by a narrow-band LFM waveform with a frequency range of 2∼3 GHz. Frequency-multiplied LFM waveforms are generated by beating the two DFB outputs. Thanks to the injection locking, the frequency-multiplied signals have excellent spurious suppression and linearity. The measured spurious suppression ratio exceeds 21.4 dB and the linearity is better than 1 × 10−5. The MF reconfigurability and the central frequency tunability are also demonstrated. A series of 20-fold frequency-multiplied LFM waveforms with different central frequencies and a 30-fold frequency-multiplied signal with a frequency range from 16 GHz to 46 GHz are generated. Moreover, a feedback setup is employed to stabilize the waveform phase against environmental interferences. The measured standard deviation of the remaining phase jitter is around 5.5 ∘ .

Accessing thermally stable solitons in microresonators generally requires complex laser tuning with a carefully selected speed. Here, we demonstrate a simplified method by manual microheater tuning with the aid of an auxiliary laser. © 2020 The Author(s).

A novel method of wideband radiofrequency signal generation is proposed based on photonic phase digitizing and heterodyne mixing. Synthesis of a linear frequency-modulated radar waveform with a bandwidth of 4 GHz is demonstrated.

A method for weak microwave signal detection based on microwave photonics-enabled single-photon technology is proposed and experimentally demonstrated, showing signal waveform and the minimum detectable signal is as low as −112.8 dBm without electrical amplifications. © 2020 The Author(s)

A hybrid radar-communication system for intelligent transportation based on optoelectronic oscillator is proposed. A code-stream with QPSK modulation of 2.4 Gb/s is generated experimentally at 24 GHz for high-speed communication and accurate ranging simultaneously.

A photonic-enabled RF self-interference cancellation system is proposed for frequency modulated continuous-wave (FMCW) radars. Simulation results show that it can realize 23-dB cancellation depth over 4-GHz instantaneous bandwidth. © 2020 The Author(s)

The distance and velocity measurement can be obtained by the round-trip time and Doppler effect on the down-chirp and the up-chirp of the linear frequency-modulated waveform (LFMW), but false targets will appear in a multi-target situation, resulting in erroneous detection. Here, we report a photonics-assisted approach to realize unambiguous simultaneous distance and velocity measurement in multi-target situations utilizing a dual-band symmetrical triangular LFMW. Dual-band observation invariance is proposed, to effectively resolve the false targets. The de-chirped signals can be obtained from parallel de-chirping processing to the dual-band echoes. By measuring and calculating the beat frequencies of the de-chirped signals in the two frequency bands, the actual parameter measurements can be acquired according to the authenticity criterion. In the experiments, detections to three targets are performed, and the distance and velocities are acquired without false targets. The absolute measurement errors of the distance and the velocity are less than 9 mm and 0.16 m/s, respectively. These results show the feasibility of the proposed approach.